1. Field of the Invention
The present invention relates to a method and an apparatus for continuous casting plants for producing strands whose cross-section is reduced during solidification.
2. Description of the Related Art
It is known in the art that strands are manufactured in such high-speed plants generally with a solidification thickness of between 18 and 450 mm and casting speeds of up to at most 15 m/min., for example, in plants for casting slabs, blooms and billets with quadratic or round profiles, wherein a reduction of the strand cross-section is preferably carried out during the solidification after the strand emerges from the mold.
This technology of casting and rolling of thin slabs or round billets is known from German patents 44 03 048, 44 03 049 and 41 39 242; in the case of thin slabs, this technology is used daily in production plants.
For example, a thin slab having a thickness of, for example, 65 mm is reduced to 40 mm in segment 0 which is arranged directly underneath the mold. This strand thickness reduction of 25 mm or 38.5% may be a disadvantage with respect to the quality of certain steels which are sensitive to internal ruptures. Thus, the internal deformation of the strand, due to the strand thickness reduction or also called casting and rolling, may trigger internal ruptures because the critical deformation of the material is exceeded at the inner strand shell liquid/solid, but also at the outer strand shell.
The above example is based on a circular arc segment 0 which has a length of 2 m and which does not introduce bending work or bending deformation into the strand shell. In this case, the deformation speed of the strand shell during casting and during solidification, which represents a measure for the strand deformation, is 1.25 mm/s at a casting speed of 6 m/min. When the casting speed is increased to, for example, 10 m/min., this value of the deformation speed increases to 2.08 mm/s and becomes very critical. Such internal deformations caused by casting and rolling are not only critical for deep drawing steel qualities which are relatively insensitive to internal deformations, but primarily for sensitive steels, such as microalloyed APX-80 qualities.
In addition, in vertical bending units in which usually bending of the strand occurs in the segment underneath the mold simultaneously with the deformation caused by casting and rolling, the bending deformation introduced into the strand is significantly increased, so that the danger of exceeding the critical deformation and, thus, the formation of cracks is even further increased.